By Dan Kaiser
With low corn and soybean prices, I have been looking at some of our long-term data to figure out how growers can reduce fertilizer costs. One study I have not spoken much about is a long-term trial that was started in 2011 at the Southwest Research and Outreach Center in Lamberton, Minnesota. Data from this study show some interesting insights on starter fertilizer containing phosphorus (P), potassium (K), and zinc.
About the study
Initially, the study was established to look at fertilizer additives used in combination with starter fertilizer, and one thing that is unique about this site is that the soil pH is very acid, testing below 5.0.
I have maintained the study over time to look at reduced rates of P and K with and without a P and K starter fertilizer in a three-year corn-corn-soybean rotation. The broadcast treatments for the first six years were similar, focused on application of removal rates of P and K for the corn crop, which resulted in a buildup of soil P from 20 to 30 ppm according to the Bray-P1 test and an increase from 150 to 200 ppm in extractable soil test K.